When we look at the countries which are hardly using any fossil fuels for electricity generation, there is one thing in common.
Their main source of electricity comes from hydro and/or nuclear power plants.
Their grid might contain some wind, geothermal and pelleted forests (aka. biomass), but those sources are only a fraction of their generation.

The main reason we do not see any country running on solar and wind alone, is that those sources are highly intermittent in another word, they are unreliable.
When the sun goes down and the wind stops, we still want to have electricity.
There are two solutions for this issue:
- Storage
which is difficult and expensive - Burn fossil gas
easy and affordable
Guess which of the two most country chooses…
We need a miracle in electricity storage technologies to be able to run on chaotic energy sources like the weather, otherwise we just reduce but not replace fossil fuel usage.

As long as cheap electricity storage is not available, our best bet is hydro and geothermal for those countries where the geology allows it and nuclear for the rest.

